Position-controlling means for gripping jaws



March 2Q, 1953 l .R. GRAY ErAL 2,632,493

- POSITION-CONTROLLING MEANS FOR GRIPPING JAWS Filed Sept/L 2, 1950 7 Sheets--Sheet 1 Snuentors AN/74N e 6M Y meer A .5M/TH, Je,

March 24, 1953 R. GRAY ET A1. 2,632,493

POSITION-CONTROLLING MEANS FOR GRIPPING JAWS Filed sept. 2, 195ov '7 sheets-sheet 2 MN mw um uw mw l I|i|||l|||||||l m, ww l 1 www@ \\NN mw INH! mw Zmventors lili/771, J1?

(Ittomeg L. R.- GRAY ETAL Mafch24, 1953.

POSITION-CONTOLLING MEANS FOR GRIPE-ING JAWS Filed sept'. 2,'1950 '7 sneets-shet 3 Sq maw NN WN Gttomeg March 24, 1953 R. GRAY ETA|.. 2,632,493

POSITION-CONTROLLING MEANS FoR GRIPPING JAWS4 Filed sept. 2, 195o 7 sheet-sheet Snventors Gtomeg March 24, 1953' L. RGRAY EAL POSITION-CONTROLLING MEANS FOR GRIPPING JAWS '7 Sheets-Sheet 6 v Filled sept. 2, 195o nventors Gttomeg w March 24, 1953 l L.; R. GRAY ET Al. 2,632,493

POSITION-CONTROLLING MEANS FOR GRIPPING JAWS Filed sept. 2, 195o 7 sheexs-sheet 'r @f ,250 T5 w14 I M nverltors B Jn/mu Gtfomeg Patented Mar. 24, ,1953

POSITION-CONTROLLING MEANS FOR GRIPPING JAWS Landon It. Gray, Redondo Beach, and Harry P. Smith, Jr., Los Angeles, Calif., assignors to Richard Seifried, Venice, Calif.

Application September 2, 1950, Serial No. 182,928

8 Claims. (Cl. 153-32) This invention relates to a machine for forming bends in elongated members and in sheets and for simultaneously stretching said members and sheets so that the same retain the bent form imparted by the machine. The present machine, disclosed in two preferred forms thereof, is an improvement of the Bending and Beveling Machine disclosed in Patent No. 2,357,027.

In said patent, cable systems, involving pulleys, a winch and a motor drive therefor, are ernployed to effect operative movement of the arms that bend a member over a die. One form of the present machine contemplates the improvement that replaces such means with simple fluid-operated cylinders enabling independent control of the movement of each arm. The other form also eliminates such cable systems and employs instead a single hydraulic cylinder that is connected to effect controlled and powerful movement of the arms. It is an object of the invention, therefore, to provide a machine of the instant character that is of simpler and more eilicient construction.

One of the forms of the present disclosure is more particularly devised for stretch-forming wide' sheets over dies of various forms wherein more stretch is imparted to a sheet at some points than at others. It is, therefore, another object f the present invention to provide an improved machine for handling such wide sheets, the same embodying novel tension cylinder means that is adapted to compensate for the varying stretch in the sheet and to control the operation and movement of the chucl that grip the ends of the sheet being stretch-formed.

Another Object of the invention is to provide a machine of the type referred to that, while quite large and of considerable mass and weight, can be easily adjusted for a particular job of work and is of such sensitivity that relatively heavy members are handled with sureness and eiiiciency and without undue strain on the machine.

The invention also has for its objects to provide such means that are positive in operation, convenient in use, easily installed in a working position vand easily disconnected therefrom, economical of manufacture, relatively simple, and of general superiority and serviceability.

The invention also comprises novel details of construction and novel combinations and ari rangements of parts, which will more fully appear in the course of the following description. However, the drawings merely show and the following description merely describes embodiments 2 of the present invention, which are given by wa of illustration or example only.

In the drawings, like reference characters designate similar parts inthe several views.

Fig. 1 is a plan view of a stretch-forming machine embodying the improvements of the present invention, the same constituting an embodiment particularly devised for handling sheets.

Fig. 2 is an enlarged front elevational view thereof with one of the sheet-bending arms swung rearwardly to another position.

Fig. 3 is an end view as seen from the left end of Fig. 2.

Fig. 4 is a further enlarged vertical sectional view as taken on line 4-4 of Fig. 3.

Fig. 5 is a fragmentary sectional view as seen from the left of Fig. 4.

Fig. 6 is a partial elevational and partial longitudinal sectional view, to the scale of Figs. 4 and 5, of one of the two tension cylinders employed in the machine.

Fig. 6a is an enlarged fragmentary sectional view as taken on line ia--Sa of Fig. 6.

Fig. 6b is a fragmentary sectional view taken on line S12-6b of Fig. 6. y

Figs. 7 and 8 are sectional detail views taken on the respective lines 1-1 and 8--8 of Fig. 6.

Fig. 9 is a plan view, with one bending arm partly broken away, of the other embodiment of the invention, the same being more particularly adapted to handle elongated members rather than sheets.

Fig. 10 is a front elevational view thereof.

Fig. 11 is an enlarged and partial cross-sectional view as taken on line I I-l I of Fig. 10.

Fig. l2 is a cross-sectional view as taken on line I2-I2 of Fig. l1.

Fig. 13 is a horizontal sectional View, to the scale of Figs. 9 and 10, the same being taken on line I3-I3 of Fig. l0.

Fig. 14 is an enlarged longitudinal sectional view of one of the two tension cylinders employed in the present embodiment.

Fig. 15 is a cross-sectional view as taken on line I5--I5 of Fig. 14.

Fig. 16 is a fragmentary front view showing means for adjusting the tension cylinders, the view being taken from the left of Fig. 15.

With particular reference to Figs. 1 to 8, inclusive, the stretch-forming machine comprises, generally, a rigid base frame 20, an adjustable die box assembly 2l carried by said frame, a. pair of swingable arm assemblies 22 on either side of the base frame, a pair of hydraulic cylinder assemblies 23, connected between the base frame and the free end of each arm assembly to swing the latter between an aligned position at the front of the machine and a parallel position alongside of the base frame, and a tension cylinder assembly 24 carried by each arm assembly and each having a sheet-,gripping jaw or clutch 25 cooperating to hold a sheet 25 for stretch-forming over a die 21 mounted on the die box 2 l The base frame Zi) is more clearly seen in Fig. 3, the same being generally C-shaped, having base and cap portions 35 and 3l, respectively ,that are horizontally disposed, and a vertical column 32 connecting said portions. Laterally directed foot brackets 33, front and back, lend stability :to lthe frame and afford means by which said frame can be bolted to a supporting surface. At the iront end of each frame portion 39 and 3i, 'there is provided a pair of bearings 35 as best seen .in Fig. 2.

Thebase frame 25, because of its large size,.is formed as a fabricated structure of welded metal platesand ina manner so 4that portions 3and3l may be connected to column 32`by`bolts 35. The upper face '3S of portion 30 and the oppositeunder face @l of portion 3l areprovided witha series of transverse and aligned key slots 38 and 39, respectively, the latter being `utilized to locate die block assemblyii relative to the open front ofthe frame. The frame is also provided with bearings di! for pivotal connection with one end of each of the hydraulic cylinder-assemblies 23, said bearings being located rearward of bearings 5d.

The die box assembly 2i slidingly iits between surfaces 35 and 3l and comprises a box il on the forward end of which is affixed a vertical wall d2 on which die 2l' is removablymounted. A'platform i3 extends forward vfrom the die boxand serves as asupport for spacers d@ on'which the die rests, the same varying in thickness, as desired, and obviating the die becoming displaced.

The rear iaceof box lil mounts a pair ofkeys 55, top and bottom, for engagement in key slots 58 and 39, said keys being mounted on pivots i5 to be swingable into and out of engagement with the slots. Simultaneous movement. of said keyson their pivots is effected through the medium of a walking-beam il and rods i5 connecting the opposite ends of said vbeam. and the respective keys. Said beam tilts on a centralpivoti and aspring 59 tilts the saine in ardireetion to project keys t5 into slots 3S and 39. The keys may be retracted or withdrawn to free the die block so that the same may be moved to adjusted position by pulling down on the longer rod t8 or up on the shorter rod. 'To hold thekeys'retracted, a captive pin 5| -mounting the arm assembly on that side. In the present case, the upper face 550i each lower arm 53 is arranged to be level with the face 35 of the base frame, and the under face 5l of each upper F arm 53, level with face 3l of said base frame. Key slots 58 and 59, respectively, are provided in faces 56 and 57 in a manner similar to the slots 38 and 39 in faces 35 and 31.

The free ends of each pair of arms 53 are con- .means .of pins 55a.

extend from a side of member 5D to a bracket 54 on each arm 53. It will be seen that the rigid triangular form of arm assemblies Z2 is achieved by connecting the ends of braces 63, as above, by The member B of each arm assembly isprovided with upper and lower exten- -sions rE55 that are -,generally horizontally aligned with the respective portions 3l) and 3i of the base frame 2U. vEach extension 65 mounts a pivot 6-6 for the :outer ends of hydraulic cylinder assemblies 23.

Said kassemblies 23 each comprise .a cylinder El onpivot di! and apiston in said cylinder and having a stem 58 `connected to pivot 66. .It will be seen that the cylinder assemblies 23extend anguiarly relative to the general disposition ofthe arm assemblies 22 so that extension or contraction of thestems 58 .will eieot pivotal movement of the arm assemblies .on their pivots 55, such relative angular disposition being achieved by the rearwardposition of ,pivots i0 and the forward position of pivots S6. It will beclear without the need for detailed description that pressure fluid may be conducted to 'one .side or the other of the pistons in cylinders 5l to contract or extend the means 23 either simultaneously or selectively to eieot simultaneousor separatepivotal movement of arm assemblies`22. 'The full lineposition of the arm assemblies in Fig. 1 represents the maximum forwardposition'thereof and, as indicated by the intermediate dot-,dash'line position, Said arm assembliesare swingable rearwardly on pivots 55 to amaximum retraction .againstthe .sides of base frame'Z.

The tension cylinder assemblies 25 are alike and, therefore, only one need be described. Fig. Gishows the same in both elevational and sectional detail. The tension cylinder assembly that is shown comprises, generally, a housing 69, a jaw Support tube assembly 'EB extending horizontally through said housing, two .similar oscillating cylinder assemblies 1i, also extending through said housing one above and one below assembly 10, ayoke i22v interconnecting assemblies 'l5 and il, Va rotation cylinder assembly l2 for rotating the ktube assembly "i5 and the jaw 25 thereon around the axis of assembly 15, and a pair of brackets i3, pivotally mounting `housing 69 and adjustable along'the'arms 53 of arm assemblies 22.

Housing 59 is formed to be generally rectangular andhas a central longitudinal bore lli therethrough for the support tube assembly l5. Above fand below bore M, the housing is provided with ksimilar bores 'i5 that each have end closures T6, said latter bores constituting cylinders and the closures having pressure fluid ports ll through which fluid is conducted into said cylinder bores l5, Upwardly and downwardly projecting and aligned trunnions 13 extend from the housing 69 and have bearing in brackets i3. An angularly directed bracket extension 'I9 is provided on the housing and is operatively connected to the lower bracket 13.

The tube assembly 'lil comprises an elongated bearing tube 8U that extends through bore l-i and is provided at one end with a clevis 8| on the cross pin 82 of which thejaw 25 is pivotally carried. The other end of tube 80 extends through 'and has rotational bearing in yoke 12a and said tube is locked to move endwise therewith by means of split abutment rings 83 and 84. Bushings 85 in bore 14 guide tube 80 for both rotational and axial movement in housing 69.

Each oscillating cylinder assembly 1| includes the mentioned cylinder bore and further comprises a hollow piston rod 86 that extends through said bore and through end closures 16. Between said closures, the rod is provided with a piston 81 that operates in bore 15. It will be clear that by admitting fluid pressure through one or the other port 11 t0 act against one side or the other of piston 81, the cylinder assemblies 1| are axially longitudinally movable relative to housing 69.

The axial movement of assemblies 1| is transmitted to tube assembly 1U by yoke 12a. To this end, a reduced portion of each rod E6 extends through bores 88 in said yoke, and an annular shoulder 89 and a split abutment ring Si) on each rod interlocks with the yoke. In addition, each rod is held against rotation as by a key 9|,

As viewed in Fig. 6, fluid admitted to the port 11 at the left of both cylinder assemblies 1| will cause movement to the right of the yoke, tube 80, and jaw 25. Fluid admitted to the ports 11 at the right will cause movement of these parts toward the left. While the system of conduits for operatively moving the jaw is not shown, the same should be clear without further explanation.

As can be seen in Fig. 2, tube 80 and rods 85, on their ends opposite t0 yoke 12a, may extend considerably beyond housing (it. To obviate deflection of these members, the same are interconnected by a deflection-reducing yoke 92. In this case, said yoke 92 is employed to support a graduated indicator 93 that moves with the yoke relative to edge 94 of the housing 69. amount of projection or retraction of the jaw 25, relative to housing 69, may be visually determined. Since tube 8|! has limited rotation, a scale 95 is ailxed to yoke 92 and an index S6 on tube 8U is associated with said scale to afford visual determination of the angle of rotation of tube 80 and, therefore, of jaw 25.

The oscillating cylinder assemblies 1| each include means for oscillating jaw 25 on its pivot 82. Said means comprises a piston 91 axially movable in a cylinder bore 98 in each rod 86, the outward movement of each said piston being limited by a gland 99. Each piston is provided with an axial cylinder bore |69 for a smaller auxiliary piston or plunger IUI that has a domed outer end and is directed to engage'against a 'pad |112 afgxed to jaw 25. Since jaw 25 has both oscillating movement on its pivot pin 82 and rotational movement around the axis of tube S0, a

compensating pad or head |62a is interposed between the domed end of each plunger 5| and respective pad |02.

Pressure fluid is admitted to cylinder bores 98 through ports H33 in both rods 86 by means of a Thus the 1| on its pivot 82 accordingly, One piston 91 will move inward into its bore 98 and the other plunger IDI would project outward in its bore to allow jaw 25 to oscillate to a position at an angle to its normal position at right angles to tube 80. As the resistance varies during a stretch-forming operation, the above-described oscillating means will adjust itself accordingly.

The angle of tilt of jaw 25 may be visually determined by a scale |04 on the'jaw and an associated index |55 extending from the clevis 8 While the details of construction of jaw 25 are not shown, it will be understood that the same comprises an elongated member having clamp elements for tightly holding an edge portion of a sheet 26 so that the two jaws of the machine mount a sheet between them as shown in Fig. l.

The rotation cylinder assembly 12 is best seen in Figs. 3, 6, 6a and 6b. The same comprises a laterally extending arm |96 aflixed to tube 80 between ring 84 and a thrust washer |1interposed between said arm and the adjacent end face |08 of yoke 12a. A cylinder |69 is pivotally carried by each hollow piston rod 86, and a piston ll in each cylinder m9 has a hollow piston rod ill) and an auxiliary plunger H3 is disposed in the hollow of rod Hl and is pivotally connected to arm |06. A port for pressure fluid is provided ior each cylinder m9 and the same are interconnected as shown at |||a in Fig. 3 so that common pressure is conducted to said cylinders. When there are no forces tending to rotate jaw 25, both pistons lia will be fully projected against shoulders H2 in cylinder |09, as in Fig. 6a. When said jaw 25 is forced by the form of die 21 to rotate in a direction to effect counterclockwise rotation of tube 8|] (as viewed in Fig. 3), auxiliary plunger ||3 of the lower cylinder |89 will project from hollow rod H0 so that uid from the upper cylinder may enter said lower cylinder to ill the hollow in rod il!) exposed by projection of the plunger therein through said common connection. There will, therefore, be a comparable retraction of the piston Illia of said upper cylinder. It will be understood that the rotation-inducing forces on jaw 25 result in compensating rotational adjustment of tube 89. Fig, 6b shows the neutral and one rotated position of jaw 25 relative to plunger IBI. Of course, the reverse of the above occurs when jaw 25 is for-ced in a clockwise direction, the plunger H3 of the upper cylinder projecting and the piston HG of the lower cylinder retracting.

Each -bracket 13 comprises a body Htl slidably engaged with the arms 53, a key H5 arranged transversely of said body to lock the same in selected and aligned key slots 58 and 59, and springurged linkage H16 normally holding said key in its slot. A manual lever ||1 is provided to selectively lock the key in place as shown, or, operate said linkage to retract the key so that brackets 13 may be moved along arms 53 to desired position.

The tension cylinder assemblies 24 are pivotally mounted on their trunnions 18. Such pivotal movement is eiected by a cylinder-piston unit I8 extending between lower bracket 13 and the mentioned extension 19 of housing 69. By supplying fluid pressure to unit H8 in the usual manner, each assembly 2Q can be swung on trunnions 1B. The dot-dash line position of assemblies 24 in Fig. 1 shows such tilting relative to brackets 13 and arms 53.

The die 21 may have different forms according to the nished shape into which a 7 sheet is to bestretch-formed. The :die .that lis shown is tapered so that its upper portion is smaller than the lower portion. It will be evident that jaws 25 will both rotate on pins 82 and oscillate withv tubes 88, as the arm assemblies are swung rearwardly by contraction of cylinder assemblies 23, as the sheet stretches over the die. Since the swinging movement of the arm assemblies is coupled with simultaneous retraction of the tension means of the tension cylinder assemblies 24, the sheet is stretched in the process of forming so as to tightly engage the die face and be formed therearound. It will be clear that rst the vertical center of the die is engaged by the sheet and then successively more lateral portions are so engaged until the sheet is completely formed. The arm assemblies can be moved to bring the ends of the sheet into parallelism or the same may be stopped at any intermediate point, as desired. Also, only one v arm assembly may be swung or said assemblies `swung through arcs of different length, as desired.

The modification shown in Figs. 9 to 16, inclusive, comprises, generally, a base frame |55, a pair of arms |5| pivotally carried on said frame, an actuating cylinder assembly |52 disposed with the base frame, a cross-head |53 movable along the base frame by the cylinder assembly |52, actuating links |54 connecting the arms |5| and the cross-head, a tension cylinder assembly |55 carried by each arm, and means |55 for effecting traverse of said assemblies |55 to a vdesired location along each respective arm |5| The base frame |55 comprises a fabricated structure having a forward frame part |51 that is provided with a table top |58 in which are formed a plurality of key grooves |55B. The top |58 is wider than frame part |51 and, as best `seen in Fig. l2, the latter is provided with bearing kbrackets |59 for pivot pins |50 `on which arms |5| are pivotally carried. Frame part |51 is provided with a front wall |6| that encloses brackets |59 from the front and also forms part of the support for said brackets. Table top |58 serves to support a die |62, the same being located as by a key |63 in 4one of the grooves |59a and, of course, is secured in place in a conventional manner.

The base frame is provided with a rearwardly extending frame part |54 that is a lower extension of frame part |51, the same including a slideway |55 along which cross-head |53 moves.

The arms |5| are alike and are arranged on their pivots to extend laterally from opposite sides of frame part |51, said arms being swingable on their pivots to a rear position parallel to frame part |64 and to each other. Each arm |5| is provided with a top plate |55 that has transverse key grooves |51. As best .seen in Fig. 13, in order that the arms may achieve the mentioned position parallel to frame part |55, each arm is provided with a through opening |68 so that the actuating links |55 may pass therethrough and connect to pivots forward of the front faces |15 of the arms. A housing groove is provided in the rear face of each arm |5| to accommodate links |55 when the dot-dash lineposition of Fig. 13 is achieved.

The actuating cylinder assembly |52 extends from frame wall |5| rearward toward, but short of, slideway |65. The same comprises a cylinder |12 in which operates a piston |13, the vlatter having a stern |14 that extends rearwardly through the end |15 of the cylinder and con- 8 nects by va pin |15 to cross-head |53. '.Pressure fluid is admitted into cylinder |12 at |11 to urge piston |13 and the cross-head rearward. Reverse movement is had by admitting pressure into the opposite end of the cylinder at |18.

The cross-head |53, as explained, is mounted to slide along slideway under control of the actuating cylinder assembly |52. The rear ends of links |55 are connected by'pins |19 to said cross-head |53 and it will be clear that rearward movement of the cross-head results in a pull on said links and forward movement results in the links being pushed. Such movement of the cross-head and links causes respective rearward and forward swing of arms |5|.

The tension cylinder assemblies |55 are alike but opposite and are shown in detail in Figs. 14 and l5. Each assembly |55 comprises, generally, a bracket |88 vmounted for adjustment along each respective arm |5| on the top yplate |65 thereof, a key |8| serving to lock said bracket in a selected key slot |61, a cylinder |82 having vertically disposed trunnions |83 engaged with the bracket so that said cylinder is mounted to swing in a horizontal plane, a piston |84 in said cylinder and having a stem 85 that extends outwardly of the cylinder in a direction toward the front of die |62 on table |58, a jaw or chuck |85 on the projecting end of each stem, and anti-rotation means |81 interconnecting the stem and cylinder to allow the former to move axially but not rotationally.

Bracket |85 has a generally C-shaped form affording upper and lower bearings |88 into which trunnions |83 extend. The key |8|, that locks the bracket to its arm, may be withdrawn endwise when adjustment of the bracket is desired, as shown in Fig. 16.

Cylinder |82 is of sturdy construction to withstand high fluid pressures, the same comprising a cylinder tube |88, one end closure |98, a second end closure |S| through which stem |85 extends, an intermediate ring |92 around tube |59, and two sets of tension rods |93 and |94, interconnecting the respective end closures and ISI with said ring. The trunnions |83 are carried by said intermediate ring |52. YIt will be understood that suitable conduits for pressure fluid are provided at the ends of the cylinder for effecting axial projection .or retraction of stem |85, as desired.

Jaw or chuck |86 comprises a cylindrical member designed to .receive and grip the end of an elongated work-piece |95 and it will be understood that the gripping portions of said jaws are especially formed according to the cross-sectional form of said work-piece. An angle-sectioned work-piece |95 is shown, but the same may have various shapes, as can be understood.

The means |81 is provided to obviate undesired rotation of the jaws or chucks, said means comprising two links |95 and |91 that are connected by a hinge |98. Link |95 is hingedly connected at |99 to cylinder closure IBI, and link |91, by a hinge 280, to a clamp ring 20| on stem |85 adjacent jaw |86.

The above-described tension cylinder assemblies |55 swing bodily with the respective arms |5| on which they are mounted. The cylinders |82 are free on their trunnions |83 and can assume an angular position relative to said arms as the arms are swung rearward in the process of bending a work-piece |95 around die |62, as shownin Ythe two operative positions of Fig. 9. While in most instances, stretch vis imparted to vthe work-piece by simultaneous retraction of jaws |86, one may be retracted more than the other, or one may be held stationary while the other is retracted, as desired.

The means |56 is provided to obviate manual handling of each tension cylinder assembly which, in the larger machines, is quite heavy. Said means comprises an electric motor 202 that drives a lead screw 263 at a low speed due to a reduction gear unit 204 interposed between the same and the motor. Said lead screw extends along the front of each arm between brackets 205 and 206 and passes through a bracket 207 depending from bracket |80. x Bracket 201 is a box-like structure that houses a nut 208 threadedly engaged with the lead screw and limits the endwise movement of said nut relative to bracket |80. Nut 208 is of a length to have end play or movement between opposed walls 209 of bracket 201. Consequently, a small amount of movement of said nut relative to bracket |80 is had before the same achieves abutment with one wall 209 or the other to effect movement of bracket |80 along its arm. Thus, torque is reduced on the motor v202 and accurate alignment oi' a stop 2|0 carried by the nut is possible so that a notch 2H in said stop can be aligned with key 18| to facilitate endwise intrusion or extraction of the latter.

While the invention that has been illustrated and described is now regarded as the preferred embodiments, the constructions are, of course, subject to modifications without departing from the spirit and scope of the invention. It is therefore not desired to restrict the invention to the particular forms of construction illustrated and described, but to cover al1 modifications that may fall within the scope of the appended claims.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. In a stretch-forming machine, a pivoted housing, a tube extending through the housing and transverse to the pivots, a pivoted workpiece-gripping jaw on one end of the tube, a yoke on the other end of said tube, and pressurefluid-operated cylinder means carried by the housing parallel to said tube and having end engagement with the jaw on either side of each pivot, said cylinder means being connected to the yoke and movable endwise to move said yoke and tube endwise.

2. In a stretch-forming machine, a pivoted housing, a tube extending through the housing and transverse to the pivots, a pivoted workpiece-gripping jaw on one end of the tube, a yoke on the other end of said tube, pressure-fluid-operated cylinder means carried by the housing parallel to said tube and having .end engagement with the jaw on either side of each pivot, said cylinder means being connected to the yoke and movable endwise to move said able in said housing, a pivot connecting the jaw and said member, and a pair of interconnected fluid-pressure-operated cylinder-piston units engaged with the jaw, one on each side of said member and .pivot and responsive to tilt of the 'jaw on its pivot to stabilize the position of the jaw when, during movement of the jaw and said member relative to the housing, one end of the jaw encounters greater resistance to movement -member and pivot and responsive to tilt of the jaw on its pivot to stabilize the position of the jaw when, during movement of the jaw and said member relative to the housing, one end of the jaw encounters greater resistance to movement than the other end, each piston-cylinder unit including an extensible and contractible pressure-uid-operated plunger engaged with the jaw.

5. In a stretch-forming machine, a workpiece-gripping jaw, a housing, a member movable in said housing, a pivot connecting the jaw and said member, a pair of interconnected fluid-pressure-operated cylinder-piston units engaged with the jaw, one on each side of said member and pivot and responsive to tilt of the jaw on its pivot to stabilize the position of the jaw when, during movement of the jaw and said member relative to the housing, one end of the jaw encounters greater resistance to movement than the otherV end, and pressure-fluidoperated means interconnecting the cylinderpiston units and said member to oscillate said member and the jaw in a plane transverse to the tilt thereof. Y y

6. A tension device for a stretch-forming machine comprising: a housing, a cylindrical member extending through and beyond both sides of the housing, a transverse pivot on one end of said cylindrical member, an elongated workpiece-engaging jaw carried by said pivot, a pair of main cylinders in said housing one on each side of the cylindrical member and parallel thereto, a main piston in each cylinder and each having a main hollow piston rod extending through and beyond both sides of the housing, the end of each main hollow piston rod adjacent the jaw having an auxiliary cylinder bore therein, an auxiliary hollow piston within each said bore, a plunger in the hollow of each auxiliary piston and directed to engage the jaw one on each side of the pivot thereof, rand a pressure-fluid conduit interconnecting the hollows of the main piston rods to transfer pressure iiuid from one main hollow piston rod to the other when the jaw is moved on its pivot in a direction to retract the plunger and auxiliary piston of said one main piston rod, the transferred fiuid in the other main piston rod simultaneously projecting the plunger of said other main piston rod to retain engagement with the jaw when moved.

7. A tension device for a stretch-forming machine comprising: a housing, a cylindrical member extending through and beyond both sides of the housing, a transverse pivot on one end of said cylindrical member, an elongated Work-piece-engagmg jaw carried bysaid pivot, a pair of main cylinders in said housing one on each side of the cylindrical member and parallel thereto, a main piston in each cylinder andl each having a. main hollow piston rod extending through and beyond both sides of the housing, a yokeconnecting said cylindrical member and the two hollow piston rods to move together under force of pressure uid admitted into the main cylinders and acting onthe main pistons therein, the end of each main hollow piston rod adjacent the jaw having an auxiliary cylinder bore therein, an auxiliary hol.- low piston within each said bore, a plunger in the hollow of each auxiliary piston and directed to engage the jaw one on each sideV of the pivot thereof, anda pressure-fluid conduit. inter-connecting the holloWs of thev main piston rods to transfer pressure. fluid from one main hollow pistonrod to the other when the jaw is moved on its pivot in a direction to retracttheplunger and auxiliary piston of said one main piston rod, the transferred fluid inthe other main piston rod simultaneously projecting the. plunger of said other main piston rodv to retain engagement with the jaw when moved.

8. A tension device for a stretch-forming machine comprising: a housing, a cylindrical member extending through and beyond both sides of the housing, a transverse pivot on one end of said cylindrical member, an elongated work-piece-engaging jaw carried by said pivot, a pair of main cylinders in said. housing one on each side. of the cylindrical member and parallel thereto, a main piston in each cylinder and each having a main hollow piston rod extending through and beyond both sides of the housing, a yoke connecting said cylindrical member and the two hollow piston rods to move together under force of. pressure fluid admitted into the main cylinders and acting on the main pistons therein, a laterally extending arm affixed to the cylindrical member adjacent said yoke, an auxiliary cylinder pivotally connected to each hollow piston rod, a hollow auxiliary piston having an elongated hollow stem operativelyv projecting from each.auxiliary` cylinder and limited for movement by a shoulder in each said auxiliary cylinder, a plunger. inthe hollow of each said stem andeachpivotally connected. to the mentionedv arm on opposite sides thereof, and a. pressure-Huid. conduit interconnecting said auxiliary cylindersto transfer pressure uid from` one to the other whenV thejaw is rotated on theaxis of` the cylindrical member'to similarly'rotate' the arm to,v thereby, retract one hollow steminto its cylinder, the plunger in the other stem simultaneously projectingunder force of uid transferred from the rst named auxiliary cylinder.

LANDON R. GRAY.

HARRY P. SMITH, JR.

REFERENCES CITED The following referencesare of record in the le of this patent:

UNITED STATESv PATENTS Number Name Date 895,438. Delany Aug. 11, 1908 1,927,580 Wisner Sept. 19, 1933 1,934,411 Dahlman Nov. 7, 1933 2,084,368 Wynn June 22, 1937 2,346,213 Flowers Apr. 1'1, 1944 2,357,027 `Sefred Aug. 29, 1944 12,365,773 Osgood Dec. 26, 1944 2,437,092 Greene Mar. 2, 1948 2,437,105 Lindsey Mar. 2, 1948 2,442,268 Fields May 25, 1948 2,487,972 Katz Nov. 15, 1949 2,515,734 Rathgen July 18, 1950 y2,515,752 Weightman July 18, 1950 2,527,412 Green Oct. 24, 1950 2,545,921 Goodwillie Mar. 20, 1951 OTHER REFERENCES P. 102 of Sept. 20, 1948, issue of Steel Mag. 

